Portable telephone units and the like portable information terminal apparatus are making remarkable evolution towards the compactness in size, lightness in weight and slimness in overall contour. So, for the semiconductor devices and other electronic components such as filter, resonator, etc., it is an essential requirement to be consistent with the above trends if they are to be adopted in such recent apparatus.
An example of such components is disclosed in Japanese Patent Laid-Open Application No. H10-270975; a surface acoustic wave device, in which the surface acoustic wave element is covered with an empty cover in the function region formed of comb-like electrodes, and is connected to a terminal electrode provided on the surface of wiring board by means of bump, and a space between the surface acoustic wave element and the wiring board is filled with resin. Also, Japanese Patent Laid-Open Application No. 2000-323603 proposes a semiconductor device in which a terminal electrode is connected direct, eliminating a wiring board, with a bump formed on electrode pad of semiconductor device, and it is sealed with resin excluding the bottom surface of terminal electrode.
In the following, some of the conventional surface acoustic wave devices and the manufacturing method are described referring to the drawings.
FIG. 16(a) is a cross sectional view showing a first example of conventional surface acoustic wave device. As shown in FIG. 16(a), a piezoelectric substrate 41 is provided on the surface with a function region 42 formed of comb-like electrodes for exciting surface acoustic wave, and an electrode pad 43 for conveying electric signal to the function region 42. Each of the electrode pads 43 is connected with corresponding terminal 44 of a package 46 via a thin metal wire 45. The thin metal wire 45 is normally made of gold, aluminum, etc. Package 46 in the present example is formed of laminated alumina ceramics 46a, 46b, 46c, and terminal 44 is electrically connected with terminal electrode 48 via an inner electrode 47. Although not illustrated in the drawing, piezoelectric substrate 41 is glued to the inside of package 46 with a resin adhesive. Package 46 is hermetically sealed with a lid 49 made of ceramic, metal, etc.
In the above-described first conventional example as shown in FIG. 16(a), however, a sufficiently large space needs to be secured in both the horizontal and vertical directions for the operation of bonding the thin metal wires 45, and respective electrode pads 43 as well as terminals 44 are requested to have a certain area that is large enough for the bonding operation. These have been material factors that hindered the device downsizing. Furthermore, a parasitic inductance intrinsic to thin metal wire 45 may deteriorate the high frequency characteristic of the element. While on the production floor, thin metal wire 45 has to be bonded one by one to connect corresponding electrode pads 43 and terminals 44. This has blocked the cost cutting efforts substantially.
Addressing the above problems, a second example is proposed for a conventional surface acoustic wave device that enables further downsizing, as shown in FIG. 16(b). In the proposed structure, a surface acoustic wave element 50 which is structured of a piezoelectric substrate 41, a function region 42 formed of comb-like electrodes, a bump electrode 53 provided on electrode pad 52, etc. is mounted with the face down. The function region 42 is covered with a space formation member 51 formed of a surrounding wall and a lid, so that a space for vibration is secured. A wiring board 54 is provided with a terminal 55 on the surface, the surface acoustic wave element 50 is connected with terminal 55 via bump electrode 53. Terminal 55 and terminal electrode 56 provided respectively on the upper surface and the bottom surface of wiring board 54 are connected via an inner electrodes 57 which is penetrating through the wiring board 54. A space between the surface acoustic wave element 50 and the wiring board 54 is filled with a resin 58 in order to enhance fixing between the two.
In the structure of FIG. 16(b), however, contact location of bump electrode 53 and location of inner electrode 57 have to be shifted sidewise to each other, since terminal 55 and terminal electrode 56 disposed respectively on the upper surface and the bottom surface of wiring board 54 are connected by inner electrode 57. Namely, because of difference in the curing/shrinking behavior between the base material of wiring board 54 and the electrode paste of inner electrode 57, the inner electrode 57 might protrude or sink in the thickness direction from the wiring board 54 during manufacturing.
In order to solve the above problem, a third example is proposed to a conventional structure, which enables to shrink the sidewise length too, as shown in FIG. 17(a).
Wiring board 54 is provided with a terminal electrode 56 which is stretching from the upper surface to the bottom surface covering the side face. Bump electrode 53 of surface acoustic wave element 50 is connected to the terminal electrode 56. Surface acoustic wave element 50 is provided with a space formation member 51 which secures a vibration space for function region 42, where surface acoustic wave excited on the main surface of piezoelectric substrate 41 propagates. Space between the surface acoustic wave element 50 and the wiring board 54 is sealed with a resin 58.
The above-configured surface acoustic wave device is manufactured through the following process steps. In the first place, a surface acoustic wave element 50 comprising a space formation member 51 covering function region 42 and a bump electrode 53, and a wiring board 54 comprising a terminal electrode 56 are prepared. These are coupled together with bump electrode 53 aligned on terminal electrode 56 and connected to. Space between surface acoustic wave element 50 and wiring board 54 is filled with a resin 58 for gluing the two together. Resin 58 enhances the gluing strength and the reliability.
In the third example of conventional surface acoustic wave device as shown in FIG. 17(a), the main surface of surface acoustic wave element 50 is sealed with resin 58, and size of the wiring board 54 can be reduced to approximately the same as that of surface acoustic wave element 50. However, reduction in the thickness is limited by the existence of a wiring board 54.
The downsizing and thickness-cutting race is proceeding rapidly also among the semiconductor devices. For this purpose, a structure as illustrated in FIG. 17(b) is proposed. A semiconductor chip 59 is provided with a bump electrode 61 formed on an electrode pad (not shown). A terminal electrode 62 is connected with the bump electrode 61. A first resin 63 is applied in a space between terminal electrode 62 and semiconductor substrate 60 with the bottom surface of terminal electrode 62 exposed. The back surface of semiconductor substrate 60 is covered with a second resin 64 for enhancing the strength and the reliability.
Process of manufacturing the above-configured semiconductor device is shown with cross sectional views in FIG. 18(a) through (e).
In the first place, a carrier 65 which is made of resin base film provided with a terminal electrode 62 formed thereon, and a semiconductor chip 59 provided with a bump electrode 61 formed on electrode pad (not shown) of semiconductor substrate 60 are prepared as shown in FIG. 18(a). Then, these two are coupled together, as illustrated in FIG. 18(b), with the bump electrode 61 aligned on the terminal electrode 62 and connected by an ultrasonic thermal compression process.
As shown in FIG. 18(c), a first resin 63 is applied surrounding the semiconductor chip 59 and the bump electrode 61, and cured to provide an under-fill. Then, as shown in FIG. 18(d), the carrier 65 is clamped from the up and down with an upper mold 66 and a lower mold 67, and a resin filling space 68 is filled with a second resin 64 to form a sealing body. And then, it is taken out of the molds, and the carrier 65 is removed. Thus, a semiconductor device protected in a chip-sized package is provided as shown in FIG. 18(e); where it is protected by a sealing body formed of first resin 63 and second resin 64, and terminal electrode 62 is exposed in the bottom surface of the sealing body.
The above-configured structure and method of manufacturing seems to be applicable also to manufacturing of a surface acoustic wave device. However, there are still a number of problems left to be solved before it is actually applied to the surface acoustic wave device.
For example, when a surface acoustic wave device is fabricated in the same configuration as the above-described semiconductor device, the overall thickness may be reduced by a thickness corresponding to the eliminated wiring substrate. But the outer edge of terminal electrode 62 is disposed recessed from the side surface of thick sealing body of resin. So, when mounting a surface acoustic wave device of the above configuration on a circuit board using a solder, a smooth solder flow is blocked by the very narrow gap between the bottom surface of sealing body and the wiring board. As a result, accuracy in the height above wiring board and the positioning accuracy of surface acoustic wave devices may be dispersed by a dispersion in shape and area among individual lands formed on a wiring board and in quantity of dispensed solder. Furthermore, due to the same reason as described above, bubbles in the molten solder are difficult to disappear during soldering on a wiring board. This may cause voids in the solder.
Application of the above method for manufacturing semiconductor devices as illustrated in FIG. 18(a) through FIG. 18(b) to the manufacture of surface acoustic wave devices further encounters following difficulty. Namely, since a resin base film is used for the carrier and each of the terminal electrodes is electrically independent, a surface acoustic wave element might suffer from pyroelectric damage caused by heat applied during the production process, from the connection of bump electrode to terminal electrode up to the step of sealing.